Typical solid dielectric shielded electrical cables include a number of copper or aluminum strands surrounded by a semiconducting or insulating strand shield, a layer of insulation, and an insulation shield. This design of solid dielectric shielded cables is known for having a useful life of 25-40 years. In some instances, the life span of a solid dielectric shielded cable is shortened when water enters the cable and forms micro-voids in the insulation layer. These micro-voids develop throughout the insulation layer in a tree-like shape, collections of which are sometimes referred to as water trees.
Water trees are known to form in the insulation layer of electrical cables when medium to high voltage alternating current is applied to a polymeric dielectric (insulator) in the presence of water and ions. As water trees grow, they compromise the dielectric properties of the polymer until the insulation layer fails. Many large water trees initiate at the site of an imperfection or a contaminant, but contamination is not a necessary condition for water trees to propagate.
Water tree growth can be eliminated or retarded by removing or minimizing the water or ions, or by reducing the voltage stress. Another approach requires the injection of dielectric enhancement fluid from an external fluid source into interstices located between the strands of the cables. U.S. Pat. No. 5,907,128 provides a detailed description of such an approach. The fluid reacts with water inside the cable and oligomerizes to form a fluid with dielectric enhancement properties. The oligomerized fluid functions as a water tree retardant and provides other beneficial properties.
One drawback to the injection of dielectric enhancement fluid is that conventional fluids produce alcohol in the process of reacting with water inside the cable. Over time and under certain conditions, the alcohols produced by the hydrolysis of the currently used dielectric enhancement fluids, under certain conditions, may cause corrosion of the cable's central aluminum conductor.
Despite the advances made in remediating electrical cables through the use of dielectric enhancement fluids, a need exists for an improved dielectric enhancement fluid that cannot result in corrosion of the cable's central conductor. The present invention seeks to fulfill this need and provides further related advantages.